I think what I need to do is the first suggestion of this - I’d like to disable the archive so I can use my own /portfolio archive page. I’m using the older Jupiter.
At the moment it grabs some kind of weird default styling. Originally I found changing the slug for the posts
works as you indicated, but then all my portfolios have a new url rather than just portfolio/portfolio page name. I don’t want to have to setup a whole heap of redirects from the old site where the urls are already live, would rather fix this one page!

Are you able to help with a way to disable the auto-archive or rename the auto-archive so that it isn’t called and my custom page with grid etc layout is?